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Plumbing in the Home/Gas Hot Water Heater Delivering Inconsistent Temperatured Water


We bought a new Rheem direct-vent gas-fired hot water heater last year to replace a Rheem which eventually failed after nearly 20 years of service. From Day 2, we have had numerous problems involving inconsistent water temperature and frequent extinguishing of the pilot. Rheem has supplied replacement parts and will be paying for repairs. However, after the gas control valve and thermocouple have been changed, the pilot stays lit, but the water remains inconsistent in that the water changes from very hot to hot to warm to lukewarm.

When I physically examine the unit, I often feel that the "hot" line is warm to very warm. However, the "cold" line is hot to very hot. There is no other heating source connected to the domestic water system. This is a one-floor home, with the hot water heater in the basement.

My specific question is: What would cause the "cold" line to be so very hot to the point that it is much hotter than the "hot" line? We suspect the hot water heater is defective based on its history, but Rheem insists all the likely at-fault parts have been changed.

Alex, My gut feeling is that your tank may have been installed improperly. The new water heaters we see here in NY come from the factory with d-electric nipples that also act as a check valves. Per manufacturers directions found in the manual, they must be installed. It is normal for the first foot or so of the cold supply to get warm during times of no hot water draw but they should not be as hot as you describe. Check to make sure the hot out let and cold inlet are connected to the proper  lines. The tank will be marked. The only other reason for the cold to get hot is a cross connection somewhere down the line or a back siphon caused by a pump of some sort. If all is checked out and found to be in order, I would install check valves in the lines going in and out and as close to the tank as possible.

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Jay Nicholas


Plumbing & Heating (warm air, hot water & steam heat)


40 years in the business, 40 years as a lic. master plumber in NY State. Retired

Graduated Magna cum laude at the School of Hard Knocks

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Commercial, residential and light industrial. You name it ...I have probably worked on it

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